System including base stations that provide information from which a mobile station can determine its position

ABSTRACT

In an embodiment, a system includes base stations and a server. Each base station has a respective fixed position, and is configured to broadcast information that a mobile station can use to determine a position of the mobile station. And the server is configured to communicate with the base stations and to track a position of a mobile station. An example of such a system is an Aeronautical Mobile Airport Communications System (AeroMACS), which includes base stations that are located in respective fixed, known positions within and around an airport, and at least one server that communicates with the base stations and tracks the positions of moveable stations within and around the airport. The base stations can provide information that allows both GNSS-enabled and non-GNSS-enabled mobile stations to determine their positions without adding significant cost or complexity to the AeroMACS.

SUMMARY

In an embodiment, a system includes base stations and a server. Eachbase station has a respective fixed position, and is configured tobroadcast information that a mobile station can use to determine aposition of the mobile station. And the server is configured tocommunicate with the base stations and to track a position of a mobilestation.

An example of such a system is an Aeronautical Mobile AirportCommunications System (AeroMACS), which is a system that complies withthe AeroMACS standard. An AeroMACS includes base stations that arelocated in respective fixed, known positions within and around anairport, and at least one server that communicates with the basestations and tracks the positions of moveable, i.e., mobile, stationswithin and around the airport. Examples of mobile stations includeairplanes, fuel trucks, baggage trucks/carts, other aircraft-servicevehicles, and even tarmac personnel such as baggage handlers. If amobile station includes an electronic positioning circuit or system foruse with a Global Navigation Satellite System (GNSS), such as the UnitedStates NAVSTAR Global Positioning System (GPS), or other satellite-basedposition system, then the base stations can be configured to broadcast,to the mobile station, information that the mobile station can use toincrease the accuracy of the mobile station's GNSS positiondetermination. And if a mobile station does not include an electronicGNSS system, then the base stations can be configured to broadcast, tothe mobile station, information from which the mobile station candetermine its position. Because the base stations are included in thesystem anyway, e.g., to allow communications between the server and themobile stations (much like cell towers allow communications between thetelephone network and mobile phones), one can configure the basestations to broadcast information from which a mobile station candetermine its position without adding significant complexity or cost toan AeroMACS.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system, such as an AeroMACS, according to anembodiment.

FIG. 2 is a diagram of a base station of the system of FIG. 1, accordingto an embodiment.

FIG. 3 is a diagram of a mobile station of FIG. 1, according to anembodiment.

FIG. 4 is a diagram of a server of the system of FIG. 1, according to anembodiment.

FIG. 5 is a diagram of base stations and the server of the system ofFIG. 1, of a GNSS-enabled mobile station of FIG. 1, and of GNSSsatellites, according to an embodiment.

FIG. 6 is a flow diagram of a method in which a base station of FIG. 5provides information that increases the accuracy of a GNSS positiondetermination made by the mobile station of FIG. 5, according to anembodiment.

FIG. 7 is a diagram of base stations and the server of the system ofFIG. 1, and of a GNSS-disabled mobile station of FIG. 1.

FIG. 8 is a flow diagram of a method in which the base stations of FIG.7 provide information from which the GNSS-disabled mobile station ofFIG. 7 can determine its position, according to an embodiment.

DETAILED DESCRIPTION

With the increase in air traffic, and thus the increase in tarmaccongestion, at some airports, it has become desirable that theseairports include a traffic-monitoring system that monitors and displays,in real time, the respective positions of all mobile stations. Examplesof a mobile station include aircraft, vehicles (e.g., baggage carts,fuel trucks, fire trucks, ambulances), and even personnel such asairport staff. Furthermore, “mobile station” can refer to, e.g., anaircraft, vehicle, or person, or can refer to the monitoring-systemelectronic circuitry onboard, or carried by, e.g., an aircraft, vehicle,or person. Such a system can, e.g., help airport operators to preventcollisions or other problems resulting from improper positioning ormovement of mobile stations, for example, by sounding an alarm, or byotherwise generating a warning, on one or more mobile stations that arein danger of colliding with each other or with another object (but thesystem may ignore potential collisions, for example, between personneland another mobile station when the other mobile station is moving atlow speed, e.g., at five miles per hour or less).

One such system for which engineers are currently developing standardsis an AeroMACS. Airport engineers envision that with an AeroMACS, amobile station will determine, periodically, its position and report itto one or more AeroMACS servers via one or more base stations that arestrategically placed in and around the airport so that wherever a mobilestation is located within or around the airport, it will be withincommunication range of at least one base station. Engineers alsoenvision that an AeroMACS will have other capabilities in addition totraffic monitoring. For example, engineers envision that an AeroMACSwill allow a mobile station to report its status (e.g., fuel level, gateassignment, whether any components are malfunctioning) to one or moreAeroMACS servers, and to receive instructions (e.g., to leave the gate,to hold its current position until further notice) and other informationfrom the one or more servers.

In today's airport environment, a mobile station, such as an airplane,determines its position using an onboard GNSS circuit or othersatellite-based position system, which includes a microprocessor ormicrocontroller, an electronic signal transmitter-receiver, and otherelectronic circuitry—hereinafter, “GNSS” refers to a global navigationsatellite system, or any other satellite-based position system, and“GNSS circuit” and “GNSS system” refer to the circuitry/system onboard amobile station for determining the mobile station's position in responseto one or more signals received from a GNSS. For a mobile station todetermine its ground position, it receives, from each of at least threeGNSS satellites, a respective signal including signal packets that eachinclude a respective time stamp and respective ephemeral data includingranging codes. The time stamp indicates at what time the correspondingGNSS satellite transmitted the signal packet, and the ephemeral dataindicates from what position the GNSS satellite transmitted the signalpacket. By comparing the time stamp from a GNSS signal packet to thetime that the mobile station received the packet, the mobile station candetermine its distance from the satellite by using the known speed c(the speed of light) of an electromagnetic signal in free space(alternatively, the mobile station's GNSS circuit can use a speed otherthan c to account for the effective impedance of the earth'satmosphere). Calculating the respective distances between the mobilestation and at least three GNSS satellites allows the mobile station'sGNSS circuit to determine, unambiguously, the ground position of themobile station. The mobile station's GNSS circuit determines the mobilestation's ground position as the point where the surfaces of threespheres intersect, each sphere having a respective one of the GNSSsatellites at its center and having a radius equal to the determineddistance between the respective GNSS satellite and the mobile station.The above explanation, and the explanations below, regarding how amobile station determines its position using GNSS are simplified forpurposes of discussion, but it is understood that a mobile station candetermine its position in any manner, no matter how complex, that iscompatible with a GNSS.

But a problem with requiring all mobile stations, such asbaggage-handling vehicles, to determine and report their positions isthat outfitting such vehicles with GNSS circuits is often prohibitivelyexpensive for a mobile station that does not already require a GNSScircuit (an example of a mobile station that may require a GNSS circuitis an aircraft).

Furthermore, even if all mobile stations are outfitted with GNSScircuits, a GNSS circuit typically can render a mobile station'sposition only with an accuracy of approximately ten meters, which, for aground-based mobile station, is equivalent to rendering the mobilestation's position within a circle having an approximately ten-meterradius from the actual position of the mobile station. Unfortunately,this level of accuracy is significantly lower than the one-meteraccuracy that the AeroMACS standard specifies for position-trackingapplications such as collision avoidance.

To increase the accuracy of a mobile station's GNSS positiondetermination, however, an AeroMACS could include a Ground BasedAugmentation System (GBAS).

As explained above, a GNSS circuit onboard a mobile station calculatesthe ground position of the mobile station by determining the propagationtimes of GNSS signal packets from at least three GNSS satellites to themobile station, and by determining the distances between the mobilestation and the GNSS satellites at the times at which the GNSSsatellites transmitted the signal packets.

For the packet-propagation-time determinations to be accurate, theclocks (one for each GNSS satellite) of the GNSS circuit onboard themobile station are synchronized with the respective clocks of the GNSSsatellites; alternatively, the GNSS circuit can include one clock thatis re-synchronized to the clock of each GNSS satellite before making therespective packet-propagation-time measurement.

But although techniques exist for synchronizing the clocks of a GNSScircuit with the GNSS satellite clocks, these techniques still typicallyyield an accuracy of only about ten meters, which is significantly worsethan the one-meter accuracy specified by the AeroMACS standard asdescribed above.

But a GBAS can improve the approximately ten-meter accuracy of a mobilestation's GNSS position determination.

A GBAS includes a ground-based GNSS station having a fixed position thatis determined, and thus known, very accurately a priori. The GNSSstation receives signals from the GNSS satellites within range of theGNSS station, synchronizes its clock/clocks with those of the GNSSsatellites in a conventional manner, determines its pseudo positionusing the GNSS signals from the satellites in a manner such as describedabove, determines a position error which is, generally, the differencebetween the pseudo position and the known actual position, and, from theposition error, determines clock corrections, and can also determinecoordinate corrections (i.e., corrections to the pseudo coordinates ofthe GNSS station). Each clock correction is the respective time (orphase) shift (positive or negative) that is added to a respective one ofthe GNSS station's clocks (or that is added to the GNSS station's singleclock for each GNSS satellite) to correct the pseudo position of theGNSS station so that it equals the known actual position of the GNSSstation. And the coordinate corrections indicate the coordinatecorrections needed to correct the pseudo position so that it equals theknown actual position of the GNSS station. The coordinate correctionscan indicate additional corrections needed to the pseudo coordinateseven after the clock corrections are applied. The GBAS GNSS station thenbroadcasts these clock corrections and coordinate corrections (e.g., inthe form of a differential-clock-correction matrix and acoordinate-correction matrix) to the GNSS-enabled mobile stations, eachof which synchronizes its clock/clocks, in a conventional manner, to theGNSS satellite clocks, and then adds the clock corrections to itssynchronized clock/clocks before determining its position, and adds thecoordinate corrections to the determined position to yield a finaldetermined position.

But there may still be problems with an AeroMACS, even if the AeroMACSincludes a GBAS.

A GBAS would be in addition to the other components of an AeroMACS, and,therefore, would add significant expense, and significant integrationcomplexity, to the AeroMACS.

Furthermore, because the GBAS GNSS station typically covers a large area(e.g., a radius of twenty three nautical miles around an airport), theaccuracies of its clock corrections can vary from mobile station tomobile station. Because the error in a mobile station's GNSSclock/clocks can vary with position and with distance from therespective GNSS satellites, the clock corrections and the coordinatecorrections from the GBAS GNSS station can be less accurate the furtheraway a mobile station is from the GBAS GNSS station.

And although including multiple GBAS GNSS stations in a AeroMACS mayimprove the overall accuracy of the correction to the mobile stations'GNSS clocks and position determination, this would increasesignificantly the cost of the GBAS and the complexities of integratingthe GBAS with the other components of the AeroMACS, and, therefore,would significantly increase the cost and complexity of the AeroMACS.

FIG. 1 is a diagram of an airport 10, which includes an AeroMACS 12 andmobile stations 14, and which can solve some or all of theabove-described problems with AeroMACS, according to an embodiment. Fora GNSS-enabled mobile station 14, i.e., a mobile station alreadyincludes a GNSS circuit, the AeroMACS 12 can eliminate the need for aGBAS, or at least can eliminate the need for a GBAS GNSS station thatdetermines and broadcasts a differential-clock-correction matrix and acoordinate-correction matrix. And for a GNSS-disabled mobile station 14,i.e., a mobile station that does not include a GNSS circuit or thatincludes a deactivated GNSS circuit, the AeroMACS 12 can provide aninfrastructure that allows the mobile station to determine and broadcastits ground position.

The AeroMACS 12 includes one or more servers 16 and one or more basestations 18, which are located at respective fixed, a-priori known,positions in and around an airport. In the described embodiment, theAeroMACS 12 includes one server 16 and multiple base stations 18, andthe positions of the base stations are accurately determined (e.g., to arange of less than one meter from a base station's actual position) in aconventional manner. Furthermore, the positions determined for the basestations can be ground-based positions (i.e., with the altitudecomponent of position set to zero), or can be three-dimensionalpositions (i.e., with altitude component allowed to have a non-zerovalue). In the described embodiment, it is assumed that the altitudecomponents of the base stations are set to zero.

The base stations 18 are configured to allow communications between theserver 16 and the mobile stations 14 much like cell towers areconfigured to allow communications between mobile phones and a cell basestation. For example, the server 16 can be configured to sendinstructions (e.g., halt, proceed, return to a home position) to amobile station 14 via the base station 18 that is closest to the mobilestation, and a mobile station 14 can be configured to send its currentposition, its status (e.g., in service, out of service, waiting for aninstruction to proceed, instructed task complete), or an acknowledgement(e.g., instruction received) to the server via the base station that isclosest to the mobile station. The base stations 18 can be configured todetermine which base station is closest to a particular mobile station,even as the mobile station is moving, in much the same way as celltowers determine which cell tower is closest to a mobile phone evenwhile the phone is moving. Furthermore, if a base station 18 closest toa mobile station 14 is out of direct communication range with the server16, then the base station can be configured to communicate with theserver via one or more intermediate base stations that are between thebase station and the server. Moreover, because the server 16 and basestations 18 are in fixed positions, they may communicate with one otherover a wired channel instead of, or in addition to, a wireless channel.

Furthermore, as described in more detail below in conjunction with FIGS.2 and 5-6, each of the base stations 18 can be configured to calculate arespective GNSS differential-clock-correction matrix and acoordinate-correction matrix, and to send the matrices to theGNSS-enabled mobile stations 14 so that the AeroMACS 12 can omit a GBAS,or at least can omit the clock-correction and coordinate-correctionfunctions of the GBAS GNSS station. Because the base stations 18 areincluded in the AeroMACS 12 already, configuring the circuitry of someor all of the base stations 18 to determine respectivedifferential-clock-correction and coordinate-correction matrices addslittle or no cost or complexity to the AeroMACS. For example, one may soconfigure the circuitry of a base station with a change to the basestation's software or firmware.

Moreover, as described in more detail below in conjunction with FIGS. 2and 6-7, the base stations 18 can be configured to broadcast pseudo GNSSsignal packets so that GNSS-disabled mobile stations 14 can determinetheir positions without the need to be fitted, or retrofitted, with aGNSS circuit. Because the base stations 18 are included in the AeroMACS12 already, configuring the circuitry of some or all of the basestations 18 to broadcast pseudo GNSS signal packets adds little or nocost or complexity to the AeroMACS. For example, one may so configurethe circuitry of a base station with a change to the base station'ssoftware or firmware. Furthermore, the circuitry on board a mobilestation 14 that determines the mobile station's position in response tothe pseudo GNSS signal packets can be less complex, can be less costly,and can consume less power than a GNSS circuit.

Still referring to FIG. 1, alternate embodiments of the AeroMACS 12 arecontemplated. For example, although it is contemplated that a systemprovider will provide the AeroMACS 12 including only the server 16, thebase stations 18, and the relative software and firmware for the serverand base stations, the system provider also can provide, and thus theAeroMACS also can include, some or all of the mobile stations 14 and thesoftware and firmware for the mobile stations. Moreover, althoughdescribed for instantiation in the airport 10, the AeroMACS 12, or asystem like the AeroMACS, can be instantiated in or on a site (e.g., awarehouse) other than an airport.

FIG. 2 is a diagram of a base station 18 of FIG. 1, according to anembodiment.

The base station 18 includes the following components: a computingcircuit 28, transmit-receive circuit 30, GNSS circuit 32, GNSSerror-correction circuit 34, position-signal generation circuit 36,mobile-station tracking circuit 38, and a bus 40, which allows theaforementioned components to communicate with one another.

The computing circuit 28 includes circuitry that is configured tocontrol the operations and the other components of the base station 18,and can be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

The transmit-receive circuit 30 includes circuitry that is configured toallow the base station 18 to communicate with the server 16 (FIG. 1) andwith one or more of the mobile stations 14 (FIG. 1), and to relaycommunications between the server and one or more of the mobilestations. For example, the transmit-receive circuit 30 can be configuredto allow such communications wirelessly over one or more frequency bandsthat are used for airport communications or that are otherwise specifiedby the AeroMACS standard. Or, because the server 16 and base stations 18are in fixed positions, the transmit-receive circuitry 30 can beconfigured for wired communication with the server. Furthermore, thetransmit-receive circuit 30 can be, or can include, one or more of aconventional instruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), or a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

The GNSS circuit 32 includes conventional GNSS circuitry that isconfigured to determine a pseudo position of the base station 18 inresponse to GNSS signals from three or more GNSS satellites. “Pseudoposition” denotes the base station's position as determined by the GNSScircuit 32, and can be different than the actual position of the basestation 18 due to errors such as a synchronization error between theclock signal(s) of the GNSS circuit 32 and the clock signals of the GNSSsatellites. Furthermore, the GNSS circuit 32 can be, or can include, oneor more of a conventional instruction-executing circuit such as amicroprocessor or microcontroller, a conventional firmware-configurablecircuit such as a field-programmable gate array (FPGA), and aconventional hardwired circuit such as an application-specificintegrated circuit (ASIC).

The GNSS error-correction circuit 34 includes circuitry that isconfigured to compare the base station's pseudo position to its actualposition, to determine, in response to the comparison, a position error,and to determine, in response to the position error, a correction to oneor more of the clock signals of the GNSS circuit 32 and coordinatecorrections after the clock corrections are applied. For example, theGNSS error-correction circuit 34 can be configured to determine theposition error equal to a difference between the pseudo position and theactual position. The correction to the clock signal(s) of the GNSScircuit 32 is such that when applied to the GNSS system clock signal(s),the pseudo position equals the actual position within a range (e.g.,one-half meter, one meter, three meters, or five meters) specified by,e.g., the AeroMACS standard, and programmed into the computing circuit.28. The GNSS error-correction circuit 34 is also configured to formatthese clock corrections (e.g., in a differential-clock-correctionmatrix) and to send the formatted clock corrections to thetransmit-receive circuit 30 for broadcast to one or more mobile stations14 (FIG. 1) that are within communication range of the base station 18.If the clock corrections do not yield the pseudo position exactly equalto the actual position, then the GNSS circuit 32 can also be configuredto generate coordinate corrections, and to send these coordinatecorrections (e.g., in a coordinate-correction matrix) to thetransmit-receive circuit 30 for broadcast to one or more mobile stations14 that are within communication range of the base station 18. Incalculating the coordinate corrections, the GNSS circuit 32 can beconfigured to take into account variables such as wind speed, and earthmovement. As described below, a GNSS-enabled mobile station 14 can usethe formatted clock corrections to correct its own GNSS clocks, and thecoordinate corrections to correct its position determination using thecorrected GNSS clocks. Furthermore, the GNSS error-correction circuit 34can be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC). Forexample, the GNSS error-correction circuit 34 can be structurally andfunctionally similar to, or the same as, a GNSS error-correction circuitof a conventional GBAS GNSS station as described above.

The position-signal generator circuit 36 includes circuitry that isconfigured to generate a position signal including packets that eachinclude a time stamp indicating the time that the packet is sent to thetransmit-receive circuit 30 for transmission, the actual position of thebase station 18, and other conventional information that allows aGNSS-disabled mobile station 14 (FIG. 1) to determine its position. Andthe circuit 36 is also configured to provide the position signal to thetransmit-receive circuit 30 for broadcast to the mobile station 14.Alternatively, because the position of the base station 18 is fixed, themobile station 14 or the server 16 may store the actual position of thebase station in, e.g., a lookup table (LUT) so that the position-signalgenerator circuit 36 need not include the base station's actual positionin the signal packets.

Furthermore, the position-signal generator circuit 36 can bestructurally and functionally similar to GNSS-satellite circuitry thatgenerates a similar position signal, but can be less complex andexpensive than GNSS-satellite circuitry. Because the position of thebase station 18 is fixed, the circuit 36 need not include circuitry fortracking the base station's position, and, as described above, may beable to forgo including the base station's position in theposition-signal packets. Furthermore, because the base station 18 ismuch closer to the mobile station 14 than are GNSS satellites, thecircuit 36 may be able to omit circuitry for encoding the positionsignal with complex error-correction codes, or for performing, on theposition signal, other signal processing that may be used for GNSSsignals. Moreover, the position-signal generator circuit 36 can be, orcan include, one or more of a conventional instruction-executing circuitsuch as a microprocessor or microcontroller, a conventionalfirmware-configurable circuit such as a field-programmable gate array(FPGA), and a conventional hardwired circuit such as anapplication-specific integrated circuit (ASIC).

Still referring to FIG. 2, the mobile-station tracking circuit 38includes circuitry that is configured to track the positions of mobilestations 14 within range of the base station 18, and, based on thetracked positions, to determine which mobile stations, if any, should belinked to the base station. The AeroMACS 12 (FIG. 1) can be designedsuch that a mobile station 14 communicates only with the closest basestation 18 (except for position determining as described below inconjunction with FIGS. 7-8). The tracking circuit 38 is configured toreceive the positions of in-range mobile stations 14, and to communicatewith other base stations (via the transmit-receive circuit 30 eitherdirectly or via the server 16) to identify the mobile stations to whichthe base station 18 is the closest base station. The tracking circuit 38is configured to cause the transmit-receive circuit 30 to then set uprespective links with the identified mobile stations 14 so that allcommunications to and from the identified mobile stations 14 comethrough the base station 18. If a mobile station 14 moves such that itbecomes closer to another base station 18, then the tracking circuits 38of the two base stations cooperate to “hand off” the mobile station fromthe former closest base station to the current closest base station.During the hand-off process, the tracking circuit 38 of the currentcloset base station 18 establishes a link to the mobile station 14, andthe tracking circuit 38 of the former closest base station 18 closes thelink to the mobile station. This track-and-hand-off process is similarto that used by cell towers when a mobile device, such as a smart phone,“roams,” i.e., moves from being closest to one cell tower to beingclosest to another cell tower. The mobile-station tracking circuit 38can be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

Still referring to FIG. 2, other embodiments of the base station 18 arecontemplated. For example, one or more of the transmit-receive circuit30, GNSS circuit 32, GNSS error-correction circuit 34, position-signalgenerator circuit 36, and mobile-station tracking circuit 38 can bepartly or wholly included within the computing circuit 30. That is, thecomputing circuit 30 can include circuitry configured to perform thefunctions of one or more of the transmit-receive circuit 30, GNSScircuit 32, GNSS error-correction circuit 34, position-signal generatorcircuit 36, and mobile-station tracking circuit 38.

FIG. 3 is a diagram of a mobile station 14 of FIG. 1, according to anembodiment.

The mobile station 14 includes the following components: a computingcircuit 48, transmit-receive circuit 50, GNSS circuit 52, non-GNSSposition-determining circuit 54, and a bus 56, which allows theaforementioned components to communicate with one another. Although themobile station 14 typically includes the non-GNSS position-determiningcircuit 54 only if the mobile station does not include the GNSS circuit52, the mobile station can include both the GNSS circuit and thenon-GNSS position-determining circuit such that the mobile station canbe selectively GNSS enabled or GNSS disabled.

The computing circuit 48 includes circuitry that is configured tocontrol the operations and the other components of the mobile station14, and can be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

The transmit-receive circuit 50 includes circuitry that is configured toallow the mobile station 14 to communicate with one or more of the basestations 18 (FIGS. 1-2), and to communicate with the server 16 directlyor via a base station (e.g., the base station closest to the mobilestation). For example, the transmit-receive circuit 50 can be configuredto allow such communications wirelessly over one or more frequency bandsthat are used for airport communications or that are otherwise specifiedby the AeroMACS standard. Furthermore, the transmit-receive circuit 50can be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), or a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

The GNSS circuit 52 includes conventional GNSS circuitry that isconfigured to determine a position of the mobile station 14 in responseto GNSS signals from three or more GNSS satellites. The GNSS circuit 52can also be configured to use the clock corrections and coordinatecorrections broadcast from one or more base stations 18 (FIGS. 1-2) toimprove the accuracy of its GNSS position determination as describedabove and as described below in conjunction with FIGS. 5-6. Becauseclock error and coordinate error can be a function of position, the GNSScircuit 52 can use only the clock corrections and coordinate correctionsbroadcast over an established link between the mobile station 14 and thebase station 18 closest to the mobile station. Or, the GNSS circuit 52can generate clock corrections and coordinate corrections from the clockcorrections broadcast by multiple closest base stations 18, e.g., by aweighted averaging of the clock corrections and the coordinatecorrections from the multiple base stations. The transmit-receivecircuit 50 can receive the clock corrections and coordinate correctionsfrom the multiple closest base stations 18 via respective links to eachof these base stations, via a link to the closest base station, or via alink to the server 16 (FIG. 1). Furthermore, if the AeroMACS 12 includesa GBAS, then the GNSS circuit 52 can be configured to use the clockcorrections and coordinate corrections broadcast from the GBAS GNSSstation as described above. Moreover, the GNSS circuit 52 can be, or caninclude, one or more of a conventional instruction-executing circuitsuch as a microprocessor or microcontroller, a conventionalfirmware-configurable circuit such as a field-programmable gate array(FPGA), and a conventional hardwired circuit such as anapplication-specific integrated circuit (ASIC).

The non-GNSS position-determining circuit 54 includes circuitry that isconfigured to determine the position of the mobile station 14 inresponse to position signals broadcast from at least three base stations18 (e.g., the three base stations closest to the mobile station) in amanner similar to the manner in which a GNSS circuit, such as the GNSScircuit 52, determines the position of a mobile station in response toposition signals broadcast from at least three GNSS satellites.

The non-GNSS position-determining circuit 54 is configured to receive,from each of at least three base stations 18 via the transmit-receivecircuit 50, a respective position signal including at least one signalpacket that each include a time stamp and that can also include aposition of the source base station. As discussed above, the time stampindicates at what time the corresponding base station 18 transmitted thesignal packet. By comparing the time stamp from the base-station signalpacket to the time that the mobile station 14 receives the packet, theposition-determining circuit 54 can determine the mobile station'sdistance from the source base station 18 by using the known speed c ofan electromagnetic signal in free space (alternatively, theposition-determining circuit can use a speed other than c to account forthe effective impedance of the earth's atmosphere). Calculating therespective distances between the mobile station 14 and at least threebase stations 18 allows the position-determining circuit 54 todetermine, unambiguously, the ground position of the mobile station. Theposition-determining circuit 54 determines the mobile station's groundposition as the point where the perimeters of at least three coplanarcircles overlap, each circle having a respective one of the basestations 18 at its center and having a radius equal to the determineddistance between the respective base station and the mobile station 14.

Although the non-GNSS position-determining circuit 54 can operate in amanner similar to that of the GNSS circuit 52, the position-determiningcircuit can be less complex and less expensive than the GNSS circuit 52.If the known fixed positions of the base stations are not included inthe signal packets, then the position-determining circuit 54 need notinclude circuitry for recovering the base-station positions from thesignal packets (as alluded to above in conjunction with FIG. 2, theposition-determining circuit 54 can store the base-station positions ina LUT, or receive them separately from the server 16). Furthermore,because the position-determining circuit 54 is configured to determinethe position of the mobile station 14 from position signals broadcast bythe ground-based base stations 18, the position-determining circuit canbe less complex than corresponding GNSS circuitry because theposition-determining circuit need only calculate intersecting circles,not intersecting spheres. Moreover, because the base stations 18 aremuch closer to the mobile station 14 than are GNSS satellites, theposition-determining circuit 54 may be able to omit circuitry fordecoding the position signal using complex error-correction codes, orfor performing, on the position signal, other signal processing that maybe used for GNSS signals. In addition, because the base stations 18 aremuch closer to the mobile station 14 than are GNSS satellites, theposition-determining circuit 54 may be able to omit circuitry forcorrecting its clock signals and coordinates, or such circuitry may beless complex than GNSS clock-correction and coordinate-correctioncircuitry. For example, the server 16 can synchronize the base-stationand mobile-station clock signals in a conventional manner, or theposition-determining circuit 54 can be configured to use a simplifiedclock-synchronizing algorithm (as compared to a GNSS clock-synchronizingalgorithm), such as the following algorithm. A base station 18 transmitsto the mobile station 14 a time stamp indicating the time of time-stamptransmission. The position-determining circuit 54 denotes the time thatit receives the time stamp from the transmit-receive circuit 50,determines a delay DELAY from the receipt time to a selected transmittime, generates a packet that includes DELAY, and then instructs thetransmit-receive circuit 50 to transmit the packet to the base station18 at the selected transmit time. Assuming that the movable station 14has moved a negligible distance during the time that the above algorithmtakes, and that there has been a negligible change in atmosphericconditions, it can be assumed that the signal-propagation time from basestation to moveable station equals the signal-propagation time frommoveable station to base station. Therefore, the base station 18determines that the total time from its transmission of the time stampto the movable station 14, to the receipt of the delay packet from themovable station 14, equals 2x+DELAY, where x is the signal-propagationtime. The base station 18 then sends another signal including a timestamp indicating the time of transmission and the determined value of x.The position-determining circuit 54 receives this signal, and “knows”that that at time of receipt, its clock should equal a time of x (plusany internal delay) ahead of the time indicated by the time stamp. Ifthe clock of the circuit 54 does not equal this time, then it can becorrected so that it would have equaled this time. In addition, theposition-determining circuit 54 can be, or can include, one or more of aconventional instruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

Still referring to FIG. 3, other embodiments of the mobile station 14are contemplated. For example, one or more of the transmit-receivecircuit 50, GNSS circuit 52, and non-GNSS position-determining circuit54 can be partly or wholly included within the computing circuit 48.That is, the computing circuit 48 can include circuitry configured toperform the functions of one or more of the transmit-receive circuit 50,GNSS circuit 52, and non-GNSS position-determining circuit 54.

FIG. 4 is a diagram of the server 16 of FIG. 1, according to anembodiment.

The server 16 includes the following components: a computing circuit 58,transmit-receive circuit 60, one or more input devices 62, one or moredata-storage devices 64, one or more output devices 66, aclock-synchronization circuit 68, and a bus 70, which allows theaforementioned components to communicate with one another.

The computing circuit 58 includes circuitry that is configured tocontrol the operations and the other components of the server 16, andcan be, or can include, one or more of a conventionalinstruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), and a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC). Thecomputing circuit 68 can also include circuitry that is configured tocontrol the operations of the mobile stations 14 (FIG. 1) and of thebase stations 18 (FIG. 1), to map the locations of the mobile stationsand base stations, and to implement one or more algorithms, such as acollision-avoidance algorithm to prevent collisions between two or moremobile stations, or between a mobile station and a base station.

The transmit-receive circuit 60 includes circuitry that is configured toallow the server 16 to communicate with the base stations 18 (FIGS. 1-2)directly or in a daisy-chain fashion, and to communicate with the mobilestations 14 directly, in a daisy-chain fashion, or via a base station(e.g., the base station closest to the mobile station). For example, thetransmit-receive circuit 60 can be configured to allow suchcommunications wirelessly over one or more frequency bands that are usedfor airport communications or that are otherwise specified by theAeroMACS standard. Or, because the server 16 and the base stations 18are in fixed positions, the transmit-receive circuitry 60 can beconfigured for wired communication with the base stations. Furthermore,the transmit-receive circuit 60 can be, or can include, one or more of aconventional instruction-executing circuit such as a microprocessor ormicrocontroller, a conventional firmware-configurable circuit such as afield-programmable gate array (FPGA), or a conventional hardwiredcircuit such as an application-specific integrated circuit (ASIC).

The one or more input devices (e.g., keyboard, mouse) 62 are configuredto allow the providing of data, programming, commands, and otherinformation to the computing circuitry 58 by, e.g., a human operator(not shown in FIG. 4).

The one or more data-storage devices (e.g., flash drive, hard diskdrive, RAM, optical drive) 64 allows for the storage of, e.g., programsand data. For example, a data-storage device 64 can be configured toimplement and to store a LUT having the positions of the base stations18 as described above.

The one or more output devices (e.g., display, printer, speaker) 66 areconfigured to allow the computing circuitry 58 to provide data in a formperceivable by a human operator.

The clock-synchronization circuit 68 includes circuitry configured tosynchronize the clock(s) of a base station's position-signal generatorcircuit 36 (FIG. 2) with the clock(s) of a mobile station's non-GNSSposition-determining circuit 54 (FIG. 3) in any suitable manner. Forexample, the circuit 68 can be configured to include a master clock(e.g., an atomic clock, or a clock synchronized to another referenceclock via, e.g., the internet), and can synchronize the base-station andmobile-station clocks to the master clock taking into account thedistances, and thus the signal-propagation delays, between the server 16and the mobile stations 14 and between the server and the base stations18.

Still referring to FIG. 4, other embodiments of the server 16 arecontemplated. For example, one or more of the transmit-receive circuit60, one or more input devices 62, one or more data-storage devices 64,one or more output devices 66, and clock-synchronization circuit 68 canbe partly or wholly included within the computing circuit 58. That is,the computing circuit 58 can include circuitry configured to perform thefunctions of one or more of the transmit-receive circuit 60, one or moreinput devices 62, one or more data-storage devices 64, one or moreoutput devices 66, and clock-synchronization circuit 68. Furthermore,the server 16 can include circuitry that is configured to generatecoordinate corrections (in the form, e.g., of a coordinate-correctionmatrix), and to send these coordinate corrections to a mobile station 14that is GNSS disabled such that the mobile station can use thecoordinate corrections in conjunction with the position signals from atleast three base stations 18 to determine its position (the mobilestation 14 can be configured to use these coordinate corrections fromthe server in a manner similar to how a GNSS-enabled mobile station 14uses coordinate corrections from a base station 18). And thesecoordinate corrections can consider variables such as wind speed andearth movement.

FIG. 5 is a diagram of a GNSS-enabled mobile station 14 (FIGS. 1 and 3),server 16 (FIGS. 1 and 4), two base stations 18 ₁-18 ₂ (FIGS. 1 and 2),and GNSS satellites 80 ₁-80 ₃, according to an embodiment. For example,the server 16 and base stations 18 can be part of the AeroMACS 12 ofFIG. 1.

FIG. 6 is a flow chart of a method that the mobile station 14 of FIG. 5can implement to determine its position using its GNSS circuit 52 (FIG.3), according to an embodiment. To reduce the cost and complexity of asystem such as the AeroMACS 12 of FIG. 1, the method uses at least onebase station 18 to correct the clocks of the mobile station's GNSScircuit 52 instead of using a GNSS station of a GBAS.

Referring to FIGS. 5-6, operation of the mobile station 14 and basestations 18 ₁ and 18 ₂ during a position-determining-and-providing modeof the mobile station is described, according to an embodiment.

At a step 90, the GNSS circuit 52 (FIG. 3) of the mobile station 14receives a GNSS packet from the GNSS satellite 80 ₁, where the packetincludes a time stamp indicating when the satellite sent the packet, andincludes information indicating the position of the satellite when thesatellite sent the packet.

Next, at a step 92, the GNSS circuit 52 of the mobile station 14requests a first clock-correction matrix from the base station 18 ₁,which is the closest base station to the mobile station. Alternately,the GNSS circuit 52 also requests a second clock-correction matrix fromthe base station 18 ₂, which is the second closest base station to themobile station. The GNSS circuit 54 may also request first, or first andsecond, coordinate-correction matrices from the base stations 18 ₁, or18 ₁ and 18 ₂, respectively.

Then, at a step 94, the base station 18 ₁ generates the firstclock-correction matrix as described above in conjunction with FIG. 2and elsewhere, and transmits, via its transmit-receive circuit 30, thematrix to the mobile station 14. And if the GNSS circuit 52 requestedthe second clock-correction matrix, then the base station 18 ₂ generatesthe second clock-correction matrix and transmits, via itstransmit-receive circuit 30, the second matrix to the mobile station 14.And if the GNSS circuit 54 requested first, or first and second,coordinate-correction matrices, then the the base station 18 ₁, or thebase stations 18 ₁ and 18 ₂, respectively, generates/generate the first,or first and second, coordinate-correction matrices, andtransmits/transmit the requested matrix/matrices to the mobile station14.

Next, at a step 96, the GNSS circuit 52 of the mobile station 14synchronizes one of its clocks with the clock of the GNSS satellite 80 ₁in a conventional manner.

Then, at a step 98, the GNSS circuit 52 of the mobile station 14 appliesto the synchronized clock a corresponding correction from the firstclock-correction matrix. Alternately, the GNSS circuit 52 can take theweighted average of the corresponding clock corrections from the firstand second clock-correction matrices, where the weighting is based onthe distances between the mobile station 14 and base stations 18 ₁ and18 ₂ (the corresponding correction from the second clock-correctionmatrix is given less weight than the corresponding correction from thefirst clock-correction matrix because the base station 18 ₂ is fartherfrom the mobile station than is the base station 18 ₁). Or the server 16can perform this weighted averaging. Continuing with this alternative,the GNSS circuit 52 then applies to its synchronized clock the weightedclock correction.

Next, at a step 100, the GNSS circuit 52 of the mobile station 14 usesthe corrected-and-synchronized clock signal to determine, in aconventional manner, the distance between the mobile station 14 and theposition of the GNSS satellite 80 ₁ at the time that the satellitetransmitted the GNSS packet.

Then, at a step 102, the GNSS circuit 52 of the mobile station 14repeats the steps 90, 96, and 98 for the other two GNSS satellites 80 ₂and 80 ₃.

Next, at a step 104, the GNSS circuit 52 of the mobile station 14conventionally determines respective equations that respectively definethe positions of the surfaces of three spheres (not shown in FIG. 5)each having a respective one of the satellites 80 at its center and eachhaving a radius equal the determined distance between the mobile station14 and the respective one of the satellites.

Then, at a step 106, the GNSS circuit 52 of the mobile station 14identifies, in a conventional manner, a point that is common to thesurfaces of all three spheres (i.e., the point where the surfaces of allthree spheres intersect), and returns the coordinates of this point asthe location of the mobile station 14. The GNSS circuit 52 can alsoapply any requested coordinate corrections (after weighted averaging ifappropriate) to the determined position before yielding a finalposition.

Next, at step 108, the mobile station 14 transmits its position, asdetermined by its GNSS circuit 52, via the transmit-receive circuit 50to the closest base station 18 ₁, which provides the determined positionto the server 16.

Still referring to FIGS. 5-6, alternate embodiments of the GNSSpositioning-determining algorithm are contemplated. For example, theGNSS circuit 52 (FIG. 3) of the mobile station 14 can determine theposition of the mobile station from more than three (e.g., four) GNSSsatellites 80. Furthermore, the GNSS circuit 52, or the server 16, candetermine a weighted clock correction from the clock corrections frommore than two base stations 18, and can determine a weighted coordinatecorrection from the coordinate corrections from more than two basestations.

FIG. 7 is a diagram of a non-GNSS-enabled mobile station 14 (FIGS. 1 and3), server 16 (FIGS. 1 and 4) and three base stations 18 ₁-18 ₃ (FIGS. 1and 2), according to an embodiment. For example, the server 16 and basestations 18 can be part of the AeroMACS 12 of FIG. 1.

FIG. 8 is a flow chart of a method that the mobile station 14 of FIG. 7can implement to determine its position without using a GNSS circuit 52(FIG. 3), according to an embodiment. For example, the mobile station 14may be, e.g., a baggage cart for which it is too expensive to outfitwith a GNSS circuit. To reduce the cost and complexity of a system suchas the AeroMACS 12 of FIG. 1, the mobile station 14 uses positionsignals from at least three base stations 18, instead of from GNSSsatellites, to determine the position of the mobile station.

Referring to FIGS. 7-8, operation of the mobile station 14 and basestations 18 ₁-18 ₃ during a non-GNSS-position-determining-and-providingmode of the mobile station is described below, according to anembodiment.

At a step 120, the non-GNSS position-determining circuit 54 (FIG. 3) ofthe mobile station 14 receives a position packet from the first basestation 18 ₁, where the packet includes a time stamp indicating when thebase station sent the packet, and includes information indicating theposition of the base station, which position is fixed. Alternatively,the circuit 54 may have the position of the base station 18 ₁ stored inan LUT, or may retrieve the position of the base station from the server16.

Next, at a step 122, the non-GNSS position-determining circuit 54 of themobile station 14 synchronizes one of its clocks with the clock of theposition-signal generator circuit 36 (FIG. 2) of the base station 18 ₁as described above in conjunction with FIG. 3, or in any other suitablemanner. Alternatively, the server 16 can perform this clocksynchronization as described above in conjunction with FIG. 4.

Then, at a step 124 the non-GNSS position-determining circuit 54 of themobile station 14 uses the synchronized clock signal to determine, in aconventional manner, the distance between the mobile station 14 and thebase station 18 ₁.

Next, at a step 126, the non-GNSS position-determining system 54 of themobile station 14 repeats the steps 120, 122, and 124 for the other twobase stations 18 ₂ and 18 ₃.

Then, at a step 128, the non-GNSS position-determining circuit 54 of themobile station 14 conventionally determines respective equations thatrespectively define the positions of the perimeters of three circles130, 132, and 134 having, at their centers, the base stations 18 ₁, 18₂, and 18 ₃, respectively, and each having a respective radius R₁, R₂,and R₃ equal the respective determined distances between the mobilestation 14 and the base stations.

Next, at a step 136, the non-GNSS position-determining circuit 54 of themobile station 14 identifies, in a conventional manner, a point that iscommon to all three perimeters of the circles 130, 132, and 134 (i.e.,the point where the perimeters of all three circles intersect), andreturns the coordinates of this point as the position of the mobilestation 14. Furthermore, the server 16 can determine coordinatecorrections taking into account, e.g., wind speed and earth movement,and the non-GNSS position-determining circuit 54 can receive thesecoordinate corrections from the server 16, and apply these coordinatecorrections to the determined position of the mobile station beforeyielding final coordinates of the position.

Then, at a step 138, the mobile station 14 transmits its position, asdetermined by its non-GNSS position-determining circuit 54, via thetransmit-receive circuit 50 to the closest base station 18 ₁, whichprovides the determined position to the server 16.

Still referring to FIGS. 7-8, alternate embodiments of the non-GNSSpositioning-determining algorithm are contemplated. For example, thenon-GNSS position-determining circuit 54 (FIG. 3) of the mobile station14 can determine the position of the mobile station from more than threebase stations 18.

From the foregoing it will be appreciated that, although specificembodiments have been described herein for purposes of illustration,various modifications may be made without deviating from the spirit andscope of the disclosure. Furthermore, where an alternative is disclosedfor a particular embodiment, this alternative may also apply to otherembodiments even if not specifically stated. Moreover, the componentsdescribed above may be disposed on a single or multiple IC dies to formone or more ICs, these one or more ICs may be coupled to one or moreother ICs. In addition, any described component or operation may beimplemented/performed in hardware, software, firmware, or a combinationof any two or more of hardware, software, and firmware. Furthermore, oneor more components of a described apparatus or system may have beenomitted from the description for clarity or another reason. Moreover,one or more components of a described apparatus or system that have beenincluded in the description may be omitted from the apparatus or system.

1-20. (canceled)
 21. A method for determining a position of one or moremobile stations using a plurality of base stations, the methodcomprising: receiving, by one or more processors, a fixed position and apseudo position of at least one base station of the plurality of basestations, wherein the pseudo position is based on a synchronizationerror between a clock signal of the at least one base station and aclock signal of a global navigation satellite system (GNSS) satellite;generating, by the one or more processors, a coordinate-correctionmatrix in response to the fixed position and the pseudo position of theat least one base station; and broadcasting, by the one or moreprocessors, the fixed position and an error in the clock signal of thebase station including the coordinate-correction matrix to a mobilestation to determine a position of the mobile station, wherein the errorin the clock signal is based on the fixed position and the pseudoposition of the at least one base station.
 22. The method of claim 21,further including: determining, by the one or more processors, aposition difference between the fixed position and the pseudo positionof the base station; and determining, by the one or more processors, theerror in the clock signal in response to the position difference. 23.The method of claim 21, further including: receiving, by the one or moreprocessors, the position of the mobile station from the mobile station,the position of the mobile station determined based the fixed positionof the at least one base station and the error in the clock signal. 24.The method of claim 21, wherein the mobile station is a GNSS-enabledmobile station.
 25. The method of claim 24, further including:broadcasting, by the one or more processors, a time stamp and the fixedposition of the at least one base station to a non-GNSS-enabled mobilestation to determine a position of the non-GNSS-enabled mobile station.26. The method of claim 25, further including: synchronizing, by the oneor more processors, a clock signal of the non-GNSS-enabled mobilestation with a clock signal of the at least one base station; andreceiving, by the one or more processors, the position of thenon-GNSS-enabled mobile station, the position of the non-GNSS-enabledmobile station determined based on the time stamp, the fixed position ofthe at least one base station, and the synchronized clock signal of thenon-GNSS-enabled mobile station.
 27. The method of claim 25, furtherincluding: generating, by the one or more processors, anon-GNSS-position coordinate-correction matrix based on wind speed andEarth movement; and broadcasting, by the one or more processors, thenon-GNSS-position coordinate-correction matrix to the non-GNSS-enabledmobile station to determine the position of the non-GNSS-enabled mobilestation.
 28. The method of claim 27, further including: receiving, bythe one or more processors, the position of the non-GNSS-enabled mobilestation, the position of the non-GNSS-enabled mobile station determinedbased on the time stamp, the fixed position of the at least one basestation, and the non-GNSS-position coordinate-correction matrix.
 29. Themethod of claim 25, wherein the at least one base station includes threeor more base stations.
 30. A system for determining a position of one ormore mobile stations using a plurality of base stations, the systemcomprising: a memory storing instructions; and one or more processorsexecuting the instructions to execute a process, the process including:receiving, by the one or more processors, a fixed position and a pseudoposition of at least one base station of the plurality of base stations,wherein the pseudo position is based on a synchronization error betweena clock signal of the at least one base station and a clock signal of aglobal navigation satellite system (GNSS) satellite; generating, by theone or more processors, a coordinate-correction matrix in response tothe fixed position and the pseudo position of the at least one basestation; and broadcasting, by the one or more processors, the fixedposition and an error in the clock signal of the base station includingthe coordinate-correction matrix to a mobile station to determine aposition of the mobile station, wherein the error in the clock signal isbased on the fixed position and the pseudo position of the at least onebase station.
 31. The system of claim 30, wherein the process furtherincludes: determining, by the one or more processors, a positiondifference between the fixed position and the pseudo position of thebase station; and determining, by the one or more processors, the errorin the clock signal in response to the position difference.
 32. Thesystem of claim 30, wherein the process further includes: receiving, bythe one or more processors, the position of the mobile station from themobile station, the position of the mobile station determined based thefixed position of the at least one base station and the error in theclock signal.
 33. The system of claim 30, wherein the mobile station isa GNSS-enabled mobile station.
 34. The system of claim 33, wherein theprocess further includes: broadcasting, by the one or more processors, atime stamp and the fixed position of the at least one base station to anon-GNSS-enabled mobile station to determine a position of thenon-GNSS-enabled mobile station.
 35. The system of claim 34, wherein theprocess further includes: synchronizing, by the one or more processors,a clock signal of the non-GNSS-enabled mobile station with a clocksignal of the at least one base station; and receiving, by the one ormore processors, the position of the non-GNSS-enabled mobile station,the position of the non-GNSS-enabled mobile station determined based onthe time stamp, the fixed position of the at least one base station, andthe synchronized clock signal of the non-GNSS-enabled mobile station.36. The system of claim 34, wherein the process further includes:generating, by the one or more processors, a non-GNSS-positioncoordinate-correction matrix based on wind speed and Earth movement; andbroadcasting, by the one or more processors, the non-GNSS-positioncoordinate-correction matrix to the non-GNSS-enabled mobile station todetermine the position of the non-GNSS-enabled mobile station.
 37. Thesystem of claim 36, wherein the process further includes: receiving, bythe one or more processors, the position of the non-GNSS-enabled mobilestation, the position of the non-GNSS-enabled mobile station determinedbased on the time stamp, the fixed position of the at least one basestation, and the non-GNSS-position coordinate-correction matrix.
 38. Thesystem of claim 34, wherein the at least one base station includes threeor more base stations.
 39. A method for determining a position of one ormore mobile stations using a plurality of base stations, the methodcomprising: receiving, by one or more processors, a fixed position and apseudo position of at least one base station of the plurality of basestations, wherein the pseudo position is based on a synchronizationerror between a clock signal of the at least one base station and aclock signal of a global navigation satellite system (GNSS) satellite;generating, by the one or more processors, a coordinate-correctionmatrix in response to the fixed position and the pseudo position of theat least one base station; broadcasting, by the one or more processors,the fixed position and an error in the clock signal of the base stationincluding the coordinate-correction matrix to a GNSS-enabled mobilestation to determine a position of the GNSS-enabled mobile station,wherein the error in the clock signal is based on the fixed position andthe pseudo position of the at least one base station; receiving, by theone or more processors, the position of the GNSS-enabled mobile stationfrom the GNSS-enabled mobile station, the position of the GNSS-enabledmobile station determined based the fixed position of the at least onebase station and the error in the clock signal; synchronizing, by theone or more processors, a clock signal of a non-GNSS-enabled mobilestation with a clock signal of the at least one base station;broadcasting, by the one or more processors, a time stamp and the fixedposition of the at least one base station to the non-GNSS-enabled mobilestation to determine a position of the non-GNSS-enabled mobile station;and receiving, by the one or more processors, the position of thenon-GNSS-enabled mobile station, the position of the non-GNSS-enabledmobile station determined based on the time stamp, the fixed position ofthe at least one base station, and the synchronized clock signal of thenon-GNSS-enabled mobile station.
 40. The method of claim 39, furtherincluding: generating, by the one or more processors, anon-GNSS-position coordinate-correction matrix based on wind speed andEarth movement; broadcasting, by the one or more processors, thenon-GNSS-position coordinate-correction matrix to the non-GNSS-enabledmobile station to determine the position of the non-GNSS-enabled mobilestation; and receiving, by the one or more processors, the position ofthe non-GNSS-enabled mobile station, the position of thenon-GNSS-enabled mobile station further determined based on thenon-GNSS-position coordinate-correction matrix.